The present invention relates generally to the recovery of zinc from solutions of metallic ions and, more particularly, to a process for selectively recovering zinc from brines containing from about 20% to about 25% by weight of dissolved solids including zinc amongst a variety of other metallic ions.
The term "brine" is commonly applied to any aqueous solution that contains a substantial quantity of dissolved metallic solids. One very common type of brine is a waste stream or byproduct stream of an industrial process. Such brines often have substantial quantities of metallic ions which can be of commercial value if recovered, such as magnesium, manganese, zinc, potassium, boron, lithium, lead, copper and silver among others. Another type of brine is that from geothermal sources below the earth's surface. With the increasing use of geothermal energy for the production of electricity, this source of brine is becoming more readily available.
Most geothermal reservoirs consist of hot liquid pools which are maintained at high pressure beneath the earth's surface. When these liquid pools are tapped for geothermal power generation, a fraction of the liquid brine is vaporized in a flash-steam power plant to produce the electricity. The remainder of the brine, which remains a liquid, is often reinjected into the geothermal reservoir. Geothermal brines typically contain numerous dissolved metals in addition to zinc, including sodium, calcium, potassium, iron, manganese, barium, strothium, magnesium, boron, lithium, lead, copper and silver. It would be commercially advantageous to process such geothermal brine prior to reinjection to recover the zinc therefrom.
Various solvent extraction processes are known for recovering zinc from solutions containing zinc in the form of the dissolved ion. For example, Canadian Pat. No. 1,026,951 discloses a two-cycle solvent extraction process for preparing a zinc solution for electrolytic deposition from a solution containing zinc and a high concentration of chloride ions. In the first cycle, zinc is extracted from the solution by means of an organic solution containing an extracting agent selected from an amine or a quaternary ammonium compound of minimum solubility in water and an organic diluent. The zinc is then re-extracted from the organic phase with an aqueous solution to obtain a zinc enriched aqueous solution. A second extraction cycle is then performed wherein the zinc enriched aqueous solution from the first cycle is reacted with an organic acid admixtured with an organic diluent. The zinc is then re-extracted from the organic phase using a strong sulphate acid solution.
Another zinc extraction process is disclosed in U.S. Pat. No. 4,203,964 wherein a kerosene solution of an organic amine or phosphorous compound is used to extract zinc from an acid chloride-bearing aqueous solution. The organic extraction solution is contacted with an aqueous solution of sulfuric acid to transfer metal ions and chloride ions to the aqueous solution. The acidified aqueous solution is then heated to drive off hydrogen chloride in water and recover the zinc as zinc sulfate.